Stereoselective construction of coconformational mechanically helical and topologically chiral [2]catenanes induced by point chirality

Significance

Mirror symmetry is a prominent feature of “coconformational mechanically helical chirality.” Nevertheless, when a topological molecule cannot be continuously deformed into its mirror image within three-dimensional space, it is classified as a topologically chiral molecule. Although there have been reports of chiral mechanically interlocked organic catenanes, the stereoselective construction of chiral cationic complexes induced by point chirality remains a significant gap in the field. To address this, we have developed a construction strategy to efficiently synthesize coconformational mechanically helical and topologically chiral [2]catenanes induced by point chirality. Our work represents a substantial advancement in the systematic preparation of complex chiral mechanically interlocked molecules and will pave the way for different research directions in chiral catalysis, sensing, and beyond.

Abstract

Supported by chiral stationary phase high-performance liquid chromatography HPLC (CSP-HPLC), examples of chiral mechanically interlocked organic molecules, including knots, rotaxanes, and catenanes, have been reported. However, the exploration of stereoselective construction of chiral cationic complexes, particularly those induced by point chirality, has been notably limited due to the constraints posed by the type of chiral chromatographic columns and separation efficiency. To address this, we have developed a construction strategy for generating coconformational mechanically helical and topologically chiral [2]catenanes through the induction of point chirality. In this study, by adjusting the symmetry of the ligand, we have easily realized the efficient construction of high-yield crystalline coconformational mechanically helical and topologically chiral [2]catenanes. Moreover, within the enantiomerically pure chiral environment of molecular self-assembly driven by L-alanine and L-valine residues in bidentate ligands, the coconformational mechanically helical and topologically chiral [2]catenanes exist exclusively as a single enantiomer, thus eliminating the need for laborious CSP-HPLC separation from racemic mixtures. The generation of the opposite enantiomer can be realized by employing unsymmetrical ligands containing corresponding D-alanine and D-valine residues, as confirmed through single-crystal X-ray diffraction, elemental analysis, electrospray-ionization time-of-flight mass spectrometry, solution-state NMR spectroscopy, and circular dichroism spectroscopy.

The high mechanical strength, elasticity, and adaptability of metal-ligand coordination bonds have significantly advanced the development of coordination-driven self-assembly. (1–4) Furthermore, inspired by the double-helix structure of DNA and the intricate folding and interactions within proteins, (5) researchers have explored the design and synthesis of complex entangled structures known as mechanically interlocked molecules (MIMs). (6–9) Among MIMs, catenanes are prominent examples, characterized by the interlocking of two or more macrocycles. (10) In their simplest form, [2]catenanes consist of two macrocyclic components, which are key supramolecular elements. Due to their unique topological structures and controllable motion, [2]catenanes exhibit a range of compelling attributes. (11–13) Through manipulation of the relative motion of the macrocyclic components within the interlocked framework in response to external stimuli, [2]catenanes have become ideal platforms for developing molecular switches and machines (14–16).

Chirality is a fundamental concept in chemistry, describing an object that cannot be superimposed onto its mirror image similar to the contrast between our left and right hands. (17, 18) In catenanes, the rocking motion of a molecular ring relative to the other molecular ring may produce coconformational mechanically helical chirality. Topological chirality extends this notion to complex molecular frameworks, describing the inherent chirality that arises from the distinctive entanglement of topological molecules in three-dimensional space. (19, 20) A topologically chiral molecule has a structure that cannot be continuously deformed into its mirror image within this three-dimensional realm. In the field of molecular self-assembly, chemists have successfully integrated chiral modifications into assembly systems. Goldup and coworkers first used a chiral auxiliary approach strategy to synthesize enantiopure topologically chiral [2]catenanes in 2019. (21) He devoted himself to the development of new synthetic methods to obtain crystalline topological chiral molecules in 2022. (22) Despite these advancements, the synthesis of topologically chiral MIMs remains challenging (23).

A singular chiral environment is crucial for achieving stereoselective synthesis of topologically chiral MIMs while avoiding complex separation procedures. (22, 24) Despite efforts to create this environment through unsymmetric synthesis methods, including the use of unsymmetric templates, catalysts, or chiral inducers, the need for subsequent separation steps remains. (25–27) A more direct approach is to use pure enantiomeric building blocks to construct topologically chiral MIMs, thereby eliminating the need for racemic mixture separation. (28–31) However, the selection of suitable chiral sources for building topologically chiral MIMs is challenging, as it is essential to maintain the integrity of the chiral structure and ensure consistent chirality throughout the MIMs assembly process. To date, achieving a stable chiral environment through point chirality for stereoselective construction of topologically chiral complexes without the need for racemic resolution remains unexplored.

Our research group has a strong interest and extensive experience in developing intricate architectures containing [Cp*Rh]²⁺ organometallic corners through coordination-driven self-assembly. (32–35) The focus of this study was to use point chirality to induce the formation of topological chirality (Fig. 1). The primary chiral ligands L1–L4 and the binuclear half-sandwich organometallic units (Rh-B) are shown in Fig. 2. We employed cost-effective and easily modifiable amino acid residues as optimal chiral sources to fabricate single chiral MIMs. Specifically, we designed semienclosed ligands (R, R)-L1 and (S, S)-L1 by linking 3, 3′-(ethyne-1,2-diyl) dianiline and 4-picolinic acid groups using L/D-alanine residues in condensation reactions. Subsequently, we derived ligands (R, R)-L3 and (S, S)-L3 by premodification of (R, R)-L1 and (S, S)-L1. Using the same synthetic strategy, the L/D-alanine residues were replaced with L/D-valine residues to obtain the semienclosed ligands (R, R)-L2, (S, S)-L2, (R, R)-L4, and (S, S)-L4. These ligands interacted with binuclear half-sandwich organometallic clips [Cp*₂Rh₂(μ-TPPHZ)(OTf)₂](OTf)₂ (Rh-B; Cp* = η⁵-pentameth-ylcyclopentadienyl; TPPHZ = tetrapyrido[3,2-a: 2′,3′ -c: 3″,2″ -h: 2‴,3‴-j]phenazine; OTf = trifluoromethanesulfonate) (Fig. 2) through aromatic stacking and hydrogen bonding interactions. We used single-crystal X-ray diffraction (XRD), electrospray ionization time-of-flight mass spectrometry (ESI–TOF/MS), elemental analysis, detailed solution-state NMR spectroscopy, and circular dichroism (CD) spectroscopy to confirm the diastereoselectivity of the synthesis, which was crucial for elucidating the coconformational mechanically helical chirality and topological chirality of the assemblies.

Fig. 1.

Construction strategy of coconformational mechanically helical and topologically chiral [2]catenanes.

Fig. 2.

Binuclear half-sandwich organometallic units Rh-B and semienclosed ligands L1–L4 are mentioned in this work.

Results and Discussion

Stereoselective Construction of Coconformational Mechanically Helical Chiral Catenanes.

Consistent with our group’s previous published works, incorporating a large π-conjugated plane group into ligand design enhanced the likelihood and the driving force (π–π stacking, C − H···O, etc.) for coordination-driven self-assembly. (28, 29, 32, 33) Thus, studies have also reported the existence of binuclear half-sandwich organometallic units, Rh-B, which possess an extensive π-conjugated plane, (36) as depicted in Fig. 2. Utilizing Sonogashira coupling, ligands (R, R)-L1 and (S, S)-L1 were synthesized to incorporate an alkyne bond between biphenyls. This design aimed to create a semirigid ligand with a broad π-conjugated plane. Furthermore, the inclusion of short peptide fragments established a stable chiral environment, thereby promoting hydrogen bonding interactions. Detailed information regarding the synthesis and characterization of these ligands is provided (SI Appendix, Experimental Section and Figs. S1–S13).

As illustrated in Fig. 3, the yellow crystalline powder Rh-1R was synthesized by reacting binuclear half-sandwich organometallic units Rh-B (0.02 mmol) with the semienclosed ligand (R, R)-L1 (0.02 mmol) in a solvent mixture of methanol (4.0 mL) and DMF (0.1 mL) at 298 K for 24 h. After concentration and filtration, the yellow crystals of Rh-1R, suitable for single-crystal XRD analysis, were obtained through slow diffusion of diethyl ether over the course of 1 wk. Single-crystal XRD analysis was then performed to precisely determine the solid-state structure of Rh-1R, as depicted in Fig. 4. The crystal was found to belong to the orthorhombic chiral P $2_1{2}_{1}2$ space group, consisting of two binuclear organometallic units Rh-B, two semienclosed ligands (R, R)-L1, and eight triflate (OTf) counter anions to balance the charge (Fig. 4A). The structure of Rh-1R is identified as a linear [2]catenane with two crossings, formed by the independent interlocking of two D-shaped binuclear macrocycles (Fig. 4B). The symmetrical linear [2]catenanes are held together by π–π stacking interactions between the binuclear half-sandwich organometallic units and the ligands, as confirmed by the single-crystal XRD analysis.

Fig. 3.

Stereoselective construction of coconformational mechanically helical chiral [2]catenanes Rh-1R, Rh-1S, Rh-2R, and Rh-2S.

Fig. 4.

(A) Chemical structure of coconformational mechanically helical chiral [2]catenanes Rh-1R based on the initially reduced structure. (B) Single-crystal X-ray crystal structure of Rh-1R. (C) ¹H NMR spectrum of Rh-1R. (D) ESI–TOF/MS spectra of Rh-1R. (E) The C − H···O hydrogen bonding interactions present in Rh-1R. Color code: C, gray; H, apple green; N, blue; Rh, turquoise. (F) CD spectra of the topologically chiral [2]catenanes Rh-1R/S in methanol solution at room temperature.

Given that the large transverse distance is sufficient to accommodate another ligand, so the distance between the alkyne bonds of ligand (R, R)-L1 and the binuclear building unit Rh-B is about 10.61 Å. Remarkably, the alkyne bonds in the structure distorted inward to achieve the optimal distance (approximately 3.28 to 3.41 Å) for π–π stacking interactions (SI Appendix, Fig. S58). The L-alanine residues at both ends of the alkynyl group also twisted unexpectedly to attain a more suitable coordination angle (approximately 102°). The angle between the two rings is about 63°, which is also an important reason for the generation of helical chirality (Fig. 4D). Furthermore, the two D-shaped binuclear macrocycles rotated at specific angles to facilitate π–π interactions and intraring C–H···O (approximately 2.11 to 2.81 Å, Fig. 4E). These noncovalent interactions, including aromatic stacking and hydrogen bonding, played a dual role: they facilitated effective chirality transfer within the ligand and stabilized the chiral metalla [2] catenanes Rh-1R, acting as driving forces for the formation of its interlocked topology.

Upon further investigation of the coconformational mechanically helical chiral [2]catenanes Rh-1R, we found that incorporating alkyne bonds into the structure not only lengthened the ligands but also enhanced the stacking interactions between the ligands and the binuclear building units. This modification significantly improved the stability of the [2]catenanes Rh-1R. Additional structural information was obtained from ESI–TOF/MS data. Notably, the peaks observed at m/z 1868.7348 and 1196.1727 correspond to [Rh-1R – 2 OTf⁻]²⁺ and [Rh-1R – 3 OTf⁻]³⁺, respectively (SI Appendix, Figs. S54–S56), further confirming the structural integrity and stability of the [2]catenanes Rh-1R.

Inspired by previous studies, (37–39) we utilized a diffusion coefficient (D) obtained from ¹H diffusion-ordered spectroscopy (DOSY) NMR to model the dimensions of Rh-1R. The ¹H DOSY NMR spectrum of Rh-1R showed a single diffusion constant (D = 2.61 × 10⁻⁶ cm² s⁻¹, SI Appendix, Fig. S53), suggesting that the structure in solution maintains a consistent size. Moreover, the measured dimensions of Rh-1R—radius length × half-height length: 14.1 Å × 11.8 Å closely matched the dimensions determined using the modified Stokes–Einstein equation, (40) which modeled the structure as a prolate spheroid (semimajor axis length × semiminor axis length: 14.1 Å × 11.6 Å, SI Appendix, Fig. S131). Further validation came from ¹H–¹H COSY NMR data (SI Appendix, Fig. S52) and additional ¹H NMR results (SI Appendix, Fig. S51), confirming that these signals correspond to the coconformational mechanically helical chiral [2]catenane Rh-1R.

To verify the stereoselective production of chiral [2]catenanes Rh-1S, we performed a simultaneous self-assembly process using the D-alanine ligand (S, S)-L1 instead of (R, R)-L1. Following a similar construction strategy, we prepared [2]catenanes Rh-1S, which is the mirror image of Rh-1R; this confirmed that Rh-1S exhibits the inverted coconformational mechanically helical chirality compared to Rh-1R, as confirmed by CD spectroscopy (Fig. 4F). The crystal structures of solid Rh-1S and Rh-1R should be similar, except the alanine residues change from L to D. This assumption is supported by elemental analysis, ESI–TOF/MS data (SI Appendix, Figs. S62–S64), and NMR spectroscopy (SI Appendix, Figs. S59–S61).

In order to ensure the universality of the construction strategy of coconformational mechanically helical chiral [2]Catenanes, we incorporated L-valine residues into our previously designed semienclosed ligands, resulting in the ligand (R, R)-L2 (SI, Experimental Section, and SI Appendix, Figs. S14–S26). Yellow cylindrical crystals of Rh-2R were prepared using the same construction strategy as Rh-1R. While a complete single-crystal structure of Rh-2R was not obtainable due to its poor quality, the elemental analysis, NMR spectroscopy (SI Appendix, Figs. S67–S69), and ESI–TOF/MS data (SI Appendix, Figs. S70–S72) confirmed its [2]catenane structure. To obtain the mirror image isomer [2]catenane Rh-2S, we used the D-valine ligand (S, S)-L2 in a simultaneous self-assembly process, replacing (R, R)-L2. Following a similar construction strategy, we successfully synthesized [2]catenane Rh-2S, which exhibited an inverted coconformational mechanically helical chirality, as confirmed by CD spectroscopy (SI Appendix, Fig. S80). The solid-state structure of Rh-2S is expected to closely mirror that of Rh-2R, with the key distinction being that valine residues are altered from L to D. This assumption was validated through elemental analysis, ESI–TOF/MS data (SI Appendix, Figs. S76–S78), and NMR spectroscopy (SI Appendix, Figs. S73–S75).

Stereoselective Construction of Topologically Chiral [2]Catenanes Induced by Point Chirality.

While previous research has successfully achieved the stereoselective construction of coconformational mechanically helical chiral [2]catenanes(mirror symmetry) through the introduction of point chirality (Fig. 5A), the structural characteristics of [2]catenanes do not inherently guarantee unconditional topological stereochemistry. However, Wasselman and Frisch (41) demonstrated that the compositional symmetry of the rings can lead to topological chirality. Notably, one of the earliest recognized mechanical stereogenic units occurs when “oriented” rings (C_nh symmetry) with a mirror plane that is parallel to the cycle are interlocked. If this orientation results from a specific sequence of atoms, for example, the highest-priority atom (blue ball, Fig. 5), sub-high-priority atom(red ball, Fig. 5), then the stereochemistry becomes a topological property of the structure, therefore such molecules have been referred to as “topologically chiral catenanes” (Fig. 5B). The absolute stereochemistry of these topologically chiral structures is invariant under all topologically permissible deformations in three-dimensional space. So, specific construction strategies are particularly important in the stereoselective synthesis of topologically chiral catenanes.

Fig. 5.

(A) The coconformational mechanically helical chirality in [2]catenanes in which coconformational isomerism is sterically prohibited. (B) The topological chirality in [2]catenanes. Note: the direction of the arrow is determined by the atomic level, according to the CIP rule, the direction is that the highest-priority atom (blue ball) rotates to the sub-high-priority atom (red ball).

According to the previous construction strategy of topologically chiral organic interlock molecules, (19, 21, 23, 24) desymmetrization of ligands can effectively solve the oriented problem of interlocking rings. So, we proposed a premodification approach to alter the symmetry of the ligands by introducing substituent groups (−CH₃) without changing the entanglement of the final structure, thereby inducing topological chirality generated by point chirality.

As illustrated in Fig. 6, the unsymmetrical ligand (R, R)-L3 (SI, Experimental Section, and SI Appendix, Figs. S27–S38), featuring an L-alanine residue as the chiral point source, was synthesized through the same reaction as (R, R)-L1. Yellow crystals Rh-3R_mt suitable for single-crystal XRD analysis were prepared using the same construction strategy as Rh-1R. Crystallographic analysis revealed that the solid-state structure of Rh-3R_mt was indeed a [2]catenane.

Fig. 6.

Stereoselective construction of topologically chiral [2]catenanes Rh-3R_mt, Rh-3S_mt, Rh-4R_mt, and Rh-4S_mt.

Due to the asymmetry of the ligand, the interlocked products also have differences in spatial orientation. To determine the relative orientation of [2]catenanes Rh-3R_mt, absolute stereochemical labels were assigned based on the orientation of each macrocycle’s polar vectors. This was achieved by tracing a path from the highest-priority atom [A, C (−CH₃), according to the Cahn-Ingold-Prelog rules (26)] to its corresponding sub-high-priority atom (B, H) (Fig. 6). With these vectors assigned, absolute stereochemistry was established by positioning the assembly so that one ring’s polar vector extended outward through the cavity of the other ring while observing the orientation of the second polar vector, clockwise was assigned R_mt, and anticlockwise was assigned S_mt. Surprisingly, we found in the crystal structure of Rh-3R_mt, that if the direction of one ring(A→B) is determined, at the same time, the direction of the other ring is clockwise(Fig. 7A). It is worth mentioning that no other topological structures were identified within the unit cell of Rh-3R_mt. Consequently, during the coordination-driven self-assembly process, the introduction of point chirality led to the creation of a stable and uniform chiral environment. This environment played a pivotal role in the high-yield construction of topologically chiral [2]catenanes Rh-3R_mt, ensuring their specific spatial orientation.

Fig. 7.

(A) Single-crystal X-ray crystal structure of the topologically chiral [2]catenanes Rh-3R_mt/S_mt. Counter anions and solvent molecules are omitted for clarity. Color code: C, gray; H, apple green; N, blue; Rh, turquoise. (B) Dimensions of Rh-3R_mt fitted by D (2.62 × 10⁻⁶ cm² s⁻¹) according to the prolate spheroidal model. (C) CD spectra of the topologically chiral [2]catenanes Rh-3R_mt/S_mt in methanol solution at room temperature.

However, comparing the structures of topologically chiral [2]catenanes Rh-3R_mt (SI Appendix, Figs. S87 and S88) and coconformational mechanically helical chiral [2]catenanes Rh-1R, we found that Rh-3R_mt has similar stability to Rh-1R. Further evidence proving the existence of the structure was obtained through elemental analysis, NMR spectroscopy, and ESI–TOF/MS.

Initially, we aimed to determine whether the solid structure of Rh-3R_mt was consistent with that of Rh-3R_mt in a methanol solution; to achieve this, we analyzed the ¹H NMR spectrum of Rh-3R_mt dissolved in a nearly saturated methanol solution with a concentration (c) of 5.0 mM relative to Cp* (SI Appendix, Fig. S81). The inherent asymmetry of the organic ligands in the complex Rh-3R_mt structure resulted in some degree of asymmetry in the cationic segment, leading to varying degrees of splitting for the hydrogen protons of the binuclear organometallic clip Rh-B. Despite this, we accurately assigned the signals to their corresponding peaks using the ¹H–¹H COSY NMR spectrum (SI Appendix, Fig. S82).

At the same time, we investigated whether the diffusion coefficients obtained from the ¹H DOSY NMR spectrum could be used to model the dimensions associated with a diffusion coefficient (D) of 2.62 × 10⁻⁶ cm² s⁻¹. This analysis could validate the structure of dissolved Rh-3R_mt. In the solid state, the Rh-3R_mt structure can be conceptualized as an ellipsoid with dimensions of 14.1 Å in radius length and 11.7 Å in half-height length (Fig. 7B). To further investigate, we used the modified prolate spheroidal-model-based Stokes–Einstein equation to calculate the corresponding ellipsoid dimensions for the given diffusion coefficient. The resulting dimensions were a semimajor axis length of 14.1 Å and a semiminor axis length of 11.6 Å (Fig. 7B), which closely resemble the molecular structural dimensions of solid Rh-3R_mt.

Furthermore, the ESI–TOF/MS data for dissolved Rh-3R_mt in methanol provided additional validation of its structure. By analyzing both the experimentally measured and theoretically simulated isotopic peak distributions, we identified the peaks at m/z 1882.7519 and 1205.5176 as corresponding to [Rh-3R_mt − 2 OTf⁻]³⁺ and [Rh-3R_mt − 3 OTf⁻]⁴⁺, respectively (SI Appendix, Figs. S85 and S86).

To validate the relative orientation of stereoselective self-assemblies, [2]catenanes Rh-3S_mt were synthesized via simultaneous self-assembly using the D-alanine ligand (S, S)-L3, replacing (R, R)-L3. Employing a similar construction strategy, we successfully prepared [2]catenanes Rh-3S_mt, which is the mirror image of Rh-3R_mt. Interestingly, crystallographic analysis revealed that when determining the direction of one ring, the direction of the other ring was consistently anticlockwise (Fig. 7A). Thus, [2]catenanes Rh-3S_mt exhibited inverted topological chirality compared to Rh-3R_mt. The spatial orientation difference between Rh-3R_mt (clockwise) and Rh-3S_mt (anticlockwise) can be attributed solely to the change from L-alanine to D-alanine residues. This conclusion was supported by elemental analysis, ESI–TOF/MS data (SI Appendix, Figs. S92–S94), and NMR spectroscopy (SI Appendix, Figs. S89–S91). Additionally, similar noncovalent interactions observed in Rh-3S_mt were also identified in Rh-3R_mt. These findings highlight the structural sensitivity of [2]catenanes to chiral alterations in amino acid residues, influencing their topological properties.

The opposite topological chirality of [2]catenanes Rh-3R_mt and Rh-3S_mt in methanol solution was further confirmed through CD spectroscopy (Fig. 7C). Combined the four chiral catenanes, Rh-1R/1S and Rh-3R_mt/3S_mt, and analyzed their corresponding peak positions. The results further confirmed the opposite chirality of Rh-1R and Rh-1S, as well as Rh-3R_mt and Rh-3S_mt, in methanol solution using CD spectroscopy (SI Appendix, Fig. S113). The CD spectra of Rh-1R and Rh-1S exhibit symmetrical curve shapes with equal but opposite signs of exciton coupling at 252, 289, and 321 nm. Similarly, the CD spectra of Rh-3R_mt and Rh-3S_mt display equal but opposite signs of exciton coupling at 243, 297, and 333 nm. Additionally, when the CD spectra of Rh-3R_mt and Rh-3S_mt are compared with those of Rh-1R and Rh-1S, the alterations in these spectra can be largely attributed to the introduction of the unsymmetric (-CH₃) group, leading to induce direction between ring and ring. So, topological chirality is generated on the basis of coconformational mechanically helical chirality. These observations underscore how subtle modifications in ligand structure can significantly impact the chiral properties of [2]catenanes.

To better validate the effectiveness and integrity of the construction strategy for topologically chiral [2]catenanes, further verification is required. We replaced the L-alanine residue with the L-valine residue and successfully obtained the unsymmetric ligand (R, R)-L4 (SI, Experimental Section, and SI Appendix, Figs. S39–S50). The same construction strategy as Rh-3R_mt is adopted. Satisfyingly, Rh-4R_mt has the same spatial conformation as Rh-3R_mt (the direction of one ring is determined, the other ring’s direction is clockwise). Elemental analysis, NMR spectroscopy (SI Appendix, Figs. S97–S99), and ESI–TOF/MS data (SI Appendix, Figs. S100–S102) confirmed this conclusion. To obtain the mirror image isomer [2]catenane Rh-4S_mt, we used the D-valine ligand (S, S)-L4 in a simultaneous self-assembly process, replacing (R, R)-L4. Following a similar construction strategy, we successfully synthesized [2]catenane Rh-4S_mt, which exhibited an inverted topological chirality, as confirmed by CD spectroscopy (SI Appendix, Fig. S112). The solid-state structure of Rh-4R_mt is expected to closely mirror that of Rh-2R, with the key distinction being that valine residues are altered from L to D. This assumption was validated through elemental analysis, NMR spectroscopy (SI Appendix, Figs. S105–S107), and ESI–TOF/MS data (SI Appendix, Figs. S108–S110).

Conclusion

In summary, the integration of various amino acid residues as point chiral sources into symmetric and unsymmetric bis-pyridyl ligands has proven effective for the controlled assembly of coconformational mechanically helical and topologically chiral [2]catenanes. By incorporating chiral amino acid residues into these ligands, a stable and consistently expressed uniform chiral environment can be established within the assembly system. This method not only eliminates the need for complex resolution processes of racemic mixtures but also significantly improves both yield and efficiency. Key factors such as solvophobic effects, π–π stacking, and hydrogen-bonding interactions are crucial in the formation of coconformational mechanically helical chiral and topologically chiral catenane structures. The construction strategy outlined here provides a valuable framework for the future synthesis of coconformational mechanically helical and topologically chiral MIMs, streamlining the process and avoiding the complexities associated with separation procedures.

Materials and Methods

General Procedure for Preparation of Coconformational Mechanically Helical Chiral [2]catenanes Rh-1R and Rh-1S.

At 298 K, a mixture solution of methanol (4.0 mL), and DMF (0.1 mL) containing Rh-B (21.4 mg, 0.02 mmol) was prepared. Ligand (R, R)-L1 (11.2 mg, 0.02 mmol) was then added to the mixture, and the resulting solution was stirred for 24 h. Subsequently, the yellow solution was evaporated to approximately 3 mL before adding diethyl ether (20 mL) to induce the formation of a yellow precipitate. The precipitate was filtered and dried, resulting in the production of a yellow crystalline solid. The synthesis method of Rh-1S was consistent with that of Rh-1R, in which Rh-1S was obtained by substituting ligand (R, R)-L1 for ligand (S, S)-L1 (11.2 mg, 0.02 mmol).

General Procedure for Preparation of Coconformational Mechanically Helical Chiral [2]catenanes Rh-2R and Rh-2S.

At 298 K, a mixture solution of methanol (4.0 mL) and DMF (0.1 mL) containing Rh-B (21.4 mg, 0.02 mmol) was prepared. Ligand (R, R)-L2 (12.3 mg, 0.02 mmol) was then added to the mixture, and the resulting solution was stirred for 24 h. The reacted solution was filtered through a membrane filter, and the obtained filtrate was crystallized via isopropyl ether diffusion to obtain yellow crystals of complex Rh-2R, which was washed with diethyl ether and dried under vacuum. Rh-2S was synthesized following the same procedure as Rh-2R, except that ligand (R, R)-L2 was replaced with ligand (S, S)-L2 (12.3 mg, 0.02 mmol).

General Procedure for Preparation of Topologically Chiral [2]catenanes Rh-3R_mt and Rh-3S_mt.

At 298 K, a mixture solution of methanol (4.0 mL) containing Rh-B (21.4 mg, 0.02 mmol) was prepared. Ligand (R, R)-L3 (11.5 mg, 0.02 mmol) was then added to the mixture, and the resulting solution was stirred for 24 h. The reacted solution was filtered through a membrane filter, and the obtained filtrate was crystallized via isopropyl ether diffusion to obtain yellow crystals of complex Rh-3R_mt, which was washed with diethyl ether and dried under a vacuum. Rh-3S_mt was synthesized following the same procedure as Rh-3R_mt, except that ligand (R, R)-L3 was replaced with ligand (S, S)-L3 (11.5 mg, 0.02 mmol).

General Procedure for Preparation of Topologically Chiral [2]catenanes Rh-4R_mt and Rh-4S_mt.

At 298 K, a mixture solution of methanol (4.0 mL) and DMF(0.1mL) containing Rh-B (21.4 mg, 0.02 mmol) was prepared. Ligand (R, R)-L4 (12.6 mg, 0.02 mmol) was then added to the mixture, and the resulting solution was stirred for 24 h. The reacted solution was filtered through a membrane filter, and the obtained filtrate was crystallized via isopropyl ether diffusion to obtain yellow crystals of complex Rh-4R_mt, which was washed with diethyl ether and dried under vacuum. Rh-4S_mt was synthesized following the same procedure as Rh-4R_mt, except that ligand (R, R)-L4 was replaced with ligand (S, S)-L4 (12.6 mg, 0.02 mmol).

X-Ray Crystal Structure Determination and Crystallographic Data.

Single crystals of Rh-1R, Rh-1S, Rh-3R_mt, Rh-3S_mt, Rh-4R_mt, and Rh-4S_mt suitable for the XRD study were obtained at room temperature. X-ray intensity data were collected at 173 K on a Bruker D8 VENTURE system. Using Olex2, the structures of Rh-1R, Rh-1S, Rh-3R_mt, Rh-3S_mt, Rh-4R_mt, and Rh-4S_mt were solved with the SHELXS-1997 structure solution program using Direct Methods and refined with the SHELXL refinement package using least-squares minimization. Single-crystal XRD data of Rh-1R (CCDC 2382653), Rh-1S (CCDC 2382654), Rh-3R_mt (CCDC 2382655), Rh-3S_mt (CCDC 2382656), Rh-4R_mt (CCDC 2382657), and Rh-4S_mt (CCDC 2382658) have been deposited in the Cambridge Crystallographic Data Centre under accession number. The details of the crystal data collection and refinement are summarized in SI Appendix, Tables S1–S3.

Supplementary Material

Appendix 01 (PDF)

Dataset S01 (TXT)

Dataset S02 (TXT)

Dataset S03 (TXT)

Dataset S04 (TXT)

Dataset S05 (TXT)

Dataset S06 (TXT)

Data, Materials, and Software Availability

Crystal data have been deposited in CCDC [CCDC 2382653 (Rh-1R) (42), 2382654 (Rh-1S) (43), 2382655 (Rh-3Rmt) (44), 2382656 (Rh-3Smt) (45), 2382657 (Rh-4Rmt) (46), and 2382658 (Rh-4Smt) (47)].